# min_difficulty (/docs/hyperparameters/min-difficulty)

`min_difficulty` is the floor under
[`difficulty`](/docs/hyperparameters/difficulty), the proof-of-work target
for PoW neuron registration. However cheap registrations get, the
difficulty controller never lets the PoW price fall below this value.
Setting it to `u64::MAX` pins difficulty at maximum, which effectively
disables PoW registration outright. Miners care because it fixes the
minimum compute cost of a PoW slot; root/governance sets it.

## How it works [#how-it-works]

Storage is `MinDifficulty` in `pallets/subtensor/src/lib.rs`, read and
written by `get_min_difficulty` / `set_min_difficulty`
(`pallets/subtensor/src/utils/misc.rs`). In the classic controller,
difficulty was rescaled each adjustment interval by how far registrations
ran over or under target, then clamped to the
\[`min_difficulty`, `max_difficulty`] band — so with quiet demand,
difficulty decayed until it sat on this floor.

The chain-wide migration `migrate_set_min_difficulty`
(`pallets/subtensor/src/migrations/migrate_set_min_difficulty.rs`) set the
floor to 10,000,000 on every subnet, matching the runtime default
(`SubtensorInitialMinDifficulty` in `runtime/src/lib.rs`).

Note that on the current runtime PoW registration is deprecated: the
`register` extrinsic routes to burned registration and no controller
adjusts `difficulty` between intervals, so this floor is dormant. The
playground below opens on a quiet-demand scenario where difficulty decays
until it sits on the bold floor line — drag the floor to its top stop (or
use the button) to see the `u64::MAX` disabled state:

<HyperparamPowDifficulty focus="min_difficulty" />

## Reading and setting [#reading-and-setting]

```
btcli sudo get --netuid N --name min_difficulty
```

Root/governance only: `sudo_set_min_difficulty` in the AdminUtils pallet
requires the root origin and takes a raw u64. It is not settable by the
subnet owner via `btcli sudo set`.

## Related [#related]

[`difficulty`](/docs/hyperparameters/difficulty) ·
[`max_difficulty`](/docs/hyperparameters/max-difficulty) ·
[`network_pow_registration_allowed`](/docs/hyperparameters/network-pow-registration-allowed) ·
[`target_regs_per_interval`](/docs/hyperparameters/target-regs-per-interval) ·
[`adjustment_interval`](/docs/hyperparameters/adjustment-interval) ·
[`min_burn`](/docs/hyperparameters/min-burn)